Surface light emitting apparatuses are conventionally used as illumination signs, displays, lighting fixtures for vehicles or buildings, and the like. There are surface light emitting apparatuses: one of which is of the backlight type where light from a light source is incident perpendicular to a light emitting surface; and the other of which is the edge-light type where light from a light source is incident substantially parallel to a light emitting surface. In recent years, edge-light type surface light emitting apparatuses have been widely adopted from the viewpoint of reductions in apparatus thickness and weight (see, for example, Patent Document 1).
There is widely known a light emitting apparatus of the above-mentioned edge-light type, including: an LED as a light source; and a light guide plate having a light guide part that guides incident light to propagate in a planar direction and a scattering part that scatters incident light toward the outside. Conventionally, a plate of transparent resin such as acrylic resin, polycarbonate or polystyrene or a plate of glass is used as the light guide part; and an ink or coating with a scattering function or the like is used as the scattering part.
It has been conventionally common to provide a single plate of resin or glass as a light guide part as mentioned above and print an ink or coating on a surface of the single plate or perform laser processing on a surface of the single plate for improvement of the scattering properties of the surface. There is however a problem that the resin plate is low in chemical resistance, weather resistance, scratch resistance and the like.
In order to solve the above problem, Patent Document 2 discloses a light guide plate in which a resin sheet having a coating of light scattering paint or ink on a surface thereof is sandwiched between and integrated with glass sheets via adhesive layers. In this patent document, the glass and resin sheets are used as a light guide part; and the light scattering paint or ink is used as a scattering part. Further, transparent resins such as acrylic resin, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), cycloolefin polymer (COP), urethane and the like are disclosed as material examples of the resin sheet used as the light guide part.
Patent Document 3 discloses a surface-emission laminated glass in which a reflection film, a light guide plate and a diffusion film are sandwiched in this order between two glass sheets and integrated together. In this patent document, the light guide plate is used as a light guide part; and the diffusion film is used as a scattering part. The light guide plate is provided to allow light to propagate therethrough by total reflection at both surfaces thereof. Plates of highly transparent resins such as acrylic resin are disclosed as examples of the light guide plate. The diffusion film is provided as a film having a light diffusion layer formed using a binder resin and a light diffusing agent or a film having a surface subjected to blast treatment. There are disclosed PET films as examples of the diffusion film.